The present invention relates to a method of sucking water and a water sucking device, more precisely relates to a method of sucking water and a water sucking device, which are capable of sucking excess water, which is used for adhering a work piece to be polished and which is included in a backing member adhered on one side face of a plate of a polishing apparatus, to remove from the backing member.
A work piece, e.g., a wafer for producing semiconductor devices, is polished by, for example, a polishing apparatus shown in FIG. 11. In the polishing apparatus shown in FIG. 11, a polishing plate 100, on which a polishing cloth 102 is adhered, is rotated in a prescribed direction. A top ring 104 is rotated in a prescribed direction and moved to and away from the polishing plate 100. A ceramic plate 106 is assembled in a head section of the top ring 104, and a wafer W is held by the plate 106 and pressed onto the polishing cloth 102 so as to polish the wafer W.
As shown in FIG. 12, a backing member 108, which is made of, for example, sheet-shaped resin foam and which is adhered on one side face of the plate 106, includes water, and the wafer W is held on the plate 106 by surface tension of the water.
These days, large and thin wafers W are used, and high polishing accuracy is required.
However, as shown in FIG. 12, a center part of a surface of the polished wafer W, which has been adhered by surface tension of the water included in the backing member adhered on the one side face of the plate 106, is apt to be thinner than an outer edge part thereof.
Namely, the center part of the surface of the polished wafer W is apt to be excessively polished, so that the wafer W is formed into a concave shape. The reason for forming the concave shape will be explained.
When the wafer W is adhered on the backing member 108 excessively including water and pressed onto the polishing cloth 102 of the polishing plate 100 so as to polish the wafer W, the backing member 108 is pressed by the outer edge part of the wafer W so that the outer edge part of the wafer W seals a space therebetween (see FIG. 13). Therefore, the excess water included in the backing member 108 cannot move to outside of the wafer W, so that the excess water concentrates to the center part of the wafer W.
At that time, temperature of the water included in the backing member 108 is risen by frictional heat caused by polishing, and a center part of the backing member 108, which corresponds to the center part of the wafer W, is made thicker than an outer edge part thereof (see FIG. 13). By firmly pressing the wafer W onto the polishing cloth 102, the wafer W is polished and formed into the concave shape.
Further, if a narrow ring-shaped template 110, which is used for preventing the wafer W so as not to remove from the backing member 108, is adhered on the plate 106 and corresponds to an outer edge of the backing member 108 (see FIG. 14), it is difficult to discharge the excess water existing inside of the template 110.
Unlike the plate 106 having no template, the excess water must be increased in the backing member 108 adhered on the plate 106 having the template 110 shown in FIG. 14.
After the wafer W is polished, the plate 106 is cleaned together with the backing member 108. Therefore, another wafer W to be newly polished is adhered onto the backing member 108 including the excess water.
Namely, the next wafer W is adhered onto the backing member 108 without drying the backing member 108, so it is difficult to adjust water content of the backing member 108 by adjusting amount of supplying water to the backing member 108.
To solve the above described problem, a method of removing excess water of a backing member adhered on a plate is disclosed in Japanese Patent Gazette No. 2003-11056. Namely, water on a holding surface of the backing member, on which the wafer is adhered, is removed by jetting air toward the holding surface of the backing member and/or rotating the plate (please see claims and FIG. 1 of JP 2003-11056).
By jetting air toward the holding surface of the backing member and/or rotating the plate, the water on the backing member can be removed.
However, generally the plate to which the backing member is adhered is cleaned together with the backing member after a wafer is polished, and another wafer is adhered onto the backing member without drying the backing member. Therefore, the backing member still includes the excess water. To remove the excess water by jetting air and/or rotating the plate, several parameters influencing the removal of the excess water, e.g., amount of jetting air, air pressure, a moving speed of an air jet nozzle, a rotational speed of the plate, must be optimized. But, it is difficult to optimize the parameters.
Further, the optimize parameters must be maintained during the polishing, so a control system must be complex.